CF351E Jeff and Permutation

Jeff's friends know full well that the boy likes to get sequences and arrays for his birthday. Thus, Jeff got sequence $ p_{1},p_{2},...,p_{n} $ for his birthday. Jeff hates inversions in sequences. An inversion in sequence $ a_{1},a_{2},...,a_{n} $ is a pair of indexes $ i,j $ $ (1

The first line contains integer $ n $ $ (1

In a single line print the answer to the problem — the minimum number of inversions Jeff can get.